Adam ;

First ~ undo the ground cable ! .

Now , look at the back of the alternator , there's a big black plastic thing , that's the combination brush holder and voltage regulator , remove both screws and gently withdraw it , if one brush is longer than the other , they're shot .

Remove the fan belts and spin the alt. by hand , if any noise or vibration no matter how minute is felt , it's junk and must needs be exchanged for another , you don't say where you're at but there's _scads_ of them in all the self service junkyards across America , $30.00 each .

Lastly , when exchanging parts , never , EVER turn in the old dead part until the job is 100 % finished and working a day or two ! they'll charge you a few $ " Core Charge " but that comes back when you take in the dead part next week , have the receipt in your hand .

-Nate